Curing polyepoxides with an acid anhydride and an acid amide



United S CURING POLYEPOXIDES WITH AN ACID ANHYDRIDE AND AN ACID AMIDE Pieter Bruin and Johannes J. Zonsveld, Amsterdam,

Netherlands, assignors to Shell Oil Company, a corporation of Delaware This invention relates to a process for curing polyepoxides. More particularly, the invention relates to a new process for curing polyepoxides with acid anhydrides using a special class of activators for the acid anhydrides, and to the resulting cured products.

Specifically, the invention provides a new process for curing and resinifying polyepoxides, and preferably the glycidyl polyethers and polyesters, which comprises mixing and reacting the polyepoxide with a carboxylic acid anhydride in the presence of an activator for the anhydride comprising an amide of the group consisting of carbon dioxide, a carboxylic acid and a sulfonic acid. The invention further provides cured products obtained by the above-described process which are characterized by their excellent hardness and durability.

It is known that acid anhydrides may be used by themselves as curing agents for such polyepoxide resins as the glycidyl polyethers of polyhydric phenols. When used by themselves, however, the anhydrides have certain undesirable properties which have placed a considerable limitation on their commercial utilization as curing agents for these polyepoxides. It has been found, for example, that the activity of the acid anhydrides in the cure of glycidyl polyethers is manifested only at relatively high temperatures. This prevents their use in the preparation of compositions that are to be cured at low temperatures or compositions that might be injured by the high temperatures. Even at the high reaction temperatures, the anhydrides in many cases act very slowly and they cannot be used in compositions which must be cured rapidly. Furthermore, the products obtained by the use of the anhydrides are sometimes deficient, particularly as to color, hardness and durability.

It is an object of the invention to provide a new method for curing polyepoxides. It is a further object to provide a new process for curing polyepoxides using acid anhydrides and a special class of activators for the anhydrides. It is a further object to provide a new process for curing polyepoxides that may be used at comparatively low temperatures. It is a further obiect to provide a process for curing polyepoxides that gives a rapid rate of cure at elevated temperatures. It is a further obiect to provide a method for curing polyepoxides that gives cured products having excellent hardness and durability. These and other objects of the invention will be apparent from the following detailed description thereof.

It has now been discovered that these and other objects are accomplished by the process of the invention comprising mixing and reacting the polyepoxide with a carboxylic acid anhydride and an activator for the anhydride comprising an amide of a member of the group consisting of carbon dioxide, a carboxylic acid and a sulfonic acid. It has been found that when the anhydrides are used in combination with the above-noted activators they display surprisingly high activity as curing agents for the polyepoxides, over a wide range of temperatures. This combination, for example, gives excellent cure of the polyepoxides at or about temperatures as lowas 60 C.

as Patm cyclic.

and does so without the liberation of large amounts of heat. The combination is thus well suited for use in the preparation of low temperature cure surface coatings and moldings and castings where a low exotherm is required. At the higher temperatures, the combination of anhydride and activator gives a very rapid rate of cure and is particularly suited for use in the preparation of rapid cure high temperature enamels and paints such as may be used on assembly lines. Additional advantage is also found in the fact that the products obtained by the use of the activators are greatly improved in hardness and durability.

I The acid an'hydrides used as the curing agent in the process of the invention may be any anhydrides derived from polycarboxylic acids which possess at least one anhydride group, i.e., a group having the structural configuration. The carboxylic acids used in the formation of the anhydrides may be saturated, unsaturated, aliphatic, cycloaliphatic, aromatic or hetero- Examples of these anhydrides include, among others, phthalic anhydride, isophthalic anhydride, di-, tetraand hexahydrophthalic anhydride, 3,4,5,6,7,7-heXa-' chloro-3,6-endomethylene 1,2,3,6-tetrahydrophthalic anhydride (chlorendic anhydride), succinic anhydride, maleic anhydride, chlorosuccinic anhydride, monochlormaleic anhydride, 6-ethyl-4-cyclohexadieney1,2-dicare boxylic acid anhydride, 3,6 dimethyl-4-cyclohexadiene-1, Z-dicarboxylic acid anhydride, 6-butyl-3,S-cycloheXadiene: 1,2-dicarboxylic acid anhydride, octadecylsuccinic acid anhydride, dodecylsuccinic acid'anhydride, dioctylsuccinie anyhydride, nonadecadienylsuccinic anhydride, 3-rnethyoxy-l.2,3,-tetrahydrophthalic acid anhydride, 3-butoxy- 1,2,3,6-tetrahydrophthalic anhydride, pyromellitic anhydride, di, tetra, and hexahydropyromellitic anhydride, polyadipic acid anhydride, polysebacic acid anhydride, and the like, and mixtures thereof.

Especially-preferred anhydrides are the normally liquid or low melting anhydrides, such as hexahydrophthalic 'an hydride. I

The activator for the anhydrides comprises the amides of a member of the group consisting of carbon dioxide, a carboxylic acid and a sulfonic acid. The amides may be aliphatic, aromatic, cycloaliphatic or heterocycliqand may be saturated or unsaturated. Examples of such amides include, but are not limited to, urea, forrnam'ide, acetamide, propionamide, n-butyramide, phthalamide, salicylamide, the naphthamides, adipamide, benzamide, benzene sulfonamide and toluene sulfonamide. l According to the process of the invention, the polyepoxide is cured by admixing and reacting the abovedescribed anhydrides and activators with the polyepoxide. The amount of the anhydride to be used the process will vary over a wide range. Good cures are obtained by reacting the polyepoxide with from 10-80% by weight of the polyepoxide, of the anhydride. For b'est're'sults, the amount of anhydride used should -be"frorn 10% to 50% by weight of the po'lyepoxide. V

The amide activators noted above are needed only in comparatively small amounts. Good results are obtained when the amide is used 'in amounts varying from 0.05% to 15% by weight of the polyepoxideyand excellent stesults can be achieved by using'0.05-l0% by weight, on the same basis. Quantities of between around 0.05% to 3% by weight, based on the polyepoxide, :are particularly preferred.

The anhydride and amide activator may be combined" together before they are added to the polyepoxide or 7 they may be added separately.

In executing the process "of the invention, it is desirable to have the polyepoxide in a mobile liquid condition .when the anhydrides and activator are added, in order to facilitate mixing. With those polyepoxides that areliquid, but too viscous for ready. mixing, one may either heat the material to reduceits viscosity or. add a liquid solvent thereto in order to provide. fluidity. Normally solid polyepoxides' are likewise either melted or mixed with a liquidsolvent. Various'solvents are suitable for achieving'thev desired fluidity They may be volatile solvents which escape from the polyepoxide composition containing the anhydride-amide mixture by evaporation before or during the curing, such ketones like acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, etc.; esters such as ethyl acetate, butyl acetate, Cellos olve acetate (ethylene, glycol monoacetate), methyl Cellosolve acetate (acetate of ethylene, glycol monomethyl ether), etc; ether alcohols, such as methyl, ethyl or butyl ether of ethylene glycol or diethylene glycol; chlorinated hydrocarbons such as trichloropropane, chloroform, etc. To save expense, these active solvents may be used in admixture with aromatic hydrocarbons such as benzene, toluene, xylene, etc., and/or alcohols, such as ethyl, isopropyl-or n-butyl alcohol. Solvents which remain in: the cured composition may also be used, such as dicthyl phthalate, dibutyl phthalate, or liquid monoepoxy compounds, including glycidyl allyl ether, glycidyl phenyl ether, styrene oxide, 1,2-hexylene oxide, glycide, and the like, as well as cyano-substituted hydrocarbons, such as acetonitrile, propionitrile,,adiponitrile, benzonitrile, and the like. It is also convenient to employ the solid or semi-solid polyepoxides in combination with a liquid polyepoxide, such as 'a normally liquid glycidyl polyether of a polyhydric alcohol. Various other ingredients may be mixed with the polyepoxide composition including pigments, fillers, dyes, plasticizers, resins, and the like. V

, The cure may be efiected over a wide range of temperatures. 'As has been indicated, the above-described anhydride-activator combinations are active at mmparatively low temperatures such as about 60 C., and the cure may be achieved by mixing the anhydride and amide activator with the polyepoxide and raising the temperature of the mixture to about this level; Excellent rates of cure are obtained atslightly higher temperatures, between about 1l0 C. to 170 C., and these are preferred for many applications where heating to such temperatures is permissible. Temperaturesmuch above 200 C. are gener ally not desirable but may be employed if necessary.

The curing agent-polyepoxide systems described above may be utilized for a great variety of important applications. Because of their low temperature cure properties,

. they are particularly useful inthe preparation of low temperature cure coating compositions, and because of their rapid high temperature cures are usefulin the forma- In these application of baking enamels and paints. tions, it is generally desirable to combine the polyepoxide with theyanhydride and amide activator and desired solvents or other'film-forming materials, and then apply this mixture to the surface to be coated. The coatings may then be allowed to set at the curing temperature. 1

The systems described above'are also very useful in the preparation of pottings and castings. They are par; ticularly suitable for preparing .very large castings which can cured at relatively low temperatures. In this application, the mixture of polyepoxide, anhydride and veniently accomplished by dissolving the anhydride and amide in acetone and mixing the solution with the polyepoxide so as to obtain a fluid mixture. The sheets of fibrous material are impregnatedwith the mixture by spreading it thereon or by dipping or otherwise immersing them in the impregnant. The solvent is conveniently removed by evaporation and the mixture is cured to the fusible resin stage. Although this operation may be conducted at low temperature, about 60 C., it is preferred to use somewhat elevated temperature such as about 1110? C to 200 C; with the impregnated sheet stock passing through or hanging free in an oven or other suitable equipment. Theresinification is arrested before in fusible product occurs by cooling'below about 40 C. A plurality of the impregnated sheets are then superposed and the assembly is curedrin a heated pressunder a pressure of about 25 to 500 or more pounds per square inch. The resulting laminate is extremely strong and resistant against the action of organic and corrosive solvents. The fibrous material used in the preparation of the laminates may be of any suitable material, such as glass cloth and matting, paper, asbestos paper, mica flakes, cotton bats, duck muslin, canvas, and the like. It is usually preferred to utilize woven glass cloth that has been given prior treatment with well known finishing or sizing agents therefor, such as chrome methacrylate or vinyl trichlorosilane.

In the above applications, the resulting cured products are characterized by their excellent hardness, durability and good water resistance, as well as by lack of discoloration which accompanies many of the other anhydride cured systems. a

The polyepoxides to be cured by use of the above "anhydrides may be saturated'or unsaturated, aliphatic,

cycloaliphatic, aromatic or heterocyclic and may be sub stituted if desired with substituents, such as chlorine atoms, hydroxyl groups, ether radicals, or the like. They may also be monomeric or polymeric.

For clarity, many of the polyepoxides and particularly those of the polymeric type will be described throughout the specification and claims in terms of'an epoxy'equivalency. The term epoxy equivalency refers to the average number of epoxy groups contained in the average molecule. This value is obtained by dividing the average molecular weight of the polyepoxide by the epoxide equivalent weight. The epoxide equivalentweight is determined. by heating a one gram sample of the polyepoxide with an excess of pyridinium chloride dissolved in pyridine. The excess pyridinium chloride is then back titrated with 0.1 .N sodium hydroxide to phenolphthalein end point. The epoxide value is calculated by considering one HCl as equivalent to one epoxide group. This method isused to obtain all epoxide values reported herein.

If the polyepoxide material consists of a single compound and all of the epoxy groups are intact the epoxy equivalency will be integers, such as 2, 3,4, and the like. However, in the case of polymeric-type polyepoxides many of the materials may contain some of the monomeric monoepoxides or have some of their epoxy groups hydrated or otherwise reacted and/ or contain macromolecules of somewhat difierent molecular Weight so the epoxy equivalency may be quite low and containing fractional values. The polymeric material may, for example, have an epoxy equivalency of 1.5, 1.8, 2.5 and the like. The polyepoxides used in the invention have an epoxy equivalency greater than 1.0.

The polyepoxides which may be used 7 th the curing 52,95 5,1 G'fi agents of this invention embrace both those polyepoxide compounds having the terminal epoxy groups and those having the internal epoxy groups The first type of polyepoxides is exemplified by such compounds as the polyglycidyl ethers, and in particular the epoxy polyethers of polyhydric phenols obtained by reacting a polyhydric phenol with a halogen-containing epoxide or dihalohydrin in the presence of an alkaline medium. Polyhydric phenols that can be used for this purpose include, among others, resorcinol, catechol, hydroquinone, methyl resorcinol, or polynuclear phenols, such as 2,2-bis(4-hyd'roxyphenyl) propane, 2,2-bis(4-hydroxy-phenol) butane, 4,4'-dihydroxybenzophenone, bis- 4-hydroxyphenol ethane, 2,2-bis(4-hydroxyphenyl) pentane, and 1,5-dihydroxynaphthalene. The halogen-containing epoxides may be further exemplified by 3-chloro- 1,2-epoxybutane, 3-bromo-l,2-epoxyhexane, 3-chloro-1,2-- epoxyoctane, and the like.

The monomer products produced by this method from dihydric phenols and epichlorohydrin may be represented by the general formula (E g- CHCHzOROCHrCfi OHz wherein R represents a divalent hydrocarbon radical of the dihydric phenol. The polymeric products will gen erally not be a single simple molecule but will be a complex mixture of glycidyl polyethers of the general formula ii o as describedabove, with any of the aforedescribedpolyhydric phenols, such 'as 'resorcinol, catechol, bis phenol, bis [4-(2-hydroxynaphth-1 yl) 2,2-hydroxynaphth-1-yl) methane and the like.

Coming under special consideration are the polyglycidyl polyethers of polyhydric alcohols obtained by reacting the polyhydric alcohol with epichlorohydrin, preferably in the presence of 0.1% to 5% by weight of an acid-acting compound, such as boron trifluoride, hydrofluoric acid, stannic chloride or'stannic acid. This reaction'is effected at about 50 C. to 125 C. with the'proportions of reactants being such that there is about one mole of epichlorohydrin for every equivalent of. hydroxyl group in the polyhydric alcohol. The resulting chlorohydrin ether is then dehydrochlorinated by heating at about 50 C. to 125 C. with a small, .e.g., 10% stoichiometrical excess of. a base, such as sodium aluminate.

The products obtained by the method shown in the preceding paragraph are polyether polyepoxide reaction products which in general contain at least three non-cyclic ether (-O) linkages, terminal epoxide-containing ether groups, and halogen attached to a carbon of an intermediate (CHZ-'(IJH) Hal group. These halogen-containing polyether polyepoxide reaction products, obtainable by partial dehydrohalogenation wherein R is a divalent hydrocarbon radical of the dihydric phenol and n is an integer of the series 0, l, 2, 3, etc. While for any single molecule of the polyether n is an integer, the fact that the result-ant polyether is a mixture of these molecules causes the determined value for n to be an average which is not necessarily zero 'or a whole number. The polyethers may in some cases contain a very small amount of material with one or both of the terminal glycidyl radicals in hydrated form.

Still a further group of the polyepoxides comprises the polyepoxy polyethers obtained by reacting, preferably in the presence of an acid-acting compound, such as hydrofluoric acid, one of the aforedescribed halogen-containing epoxides with a polyhydric alcohol, and subsequently treating the resulting product with an alkaline component. Polyhydric alcohols that may be used for this purpose. include glycerol, propylene glycol, ethylene glycol, .diethylene glycol, butylene glycol, hexanetriol, sorbitol, mannitol, pentanetriol, pentaerythritol, diand tripentaerythritol, polyglycerol, dulcitol, inositol, carbohydrates, methyltrlmethylolpropane, 2,6-octanediol, 1,2,4,5-tetrahydroxycyclohexane, 2-ethylhexanetriol-l,2,6, glycerol methyl ether, glycerol allyl ether, polyvinyl alcohol and polyallyl alcohol, and mixtures thereof. Such polyepoxides may be exemplified by glycerol triglycidyl ether, mannitol tetraglycidyl ether, pentaerythritol tetraglycidyl ether and sorbitol tetraglycidyl ether.

A further group of the polyepoxides comprises the polyepoxy polyesters obtained by esterifying a polycarboxylic acid with an epoxy-containing alcohol, such as, for example, the diglycidyl ester of adipic acid, the diglycidyl ester of malonic acid, and the diglycidyl ester of succinic acid.

A group of polymeric-type polyepoxides comprises the hydroxy-substituted polyepoxy polyethers obtained by reacting, preferably in an alkaline medium, a slight excess, e.g., .5 to 3 mol excess, of a halogen-containing epoxide of polyhalohydrin alcohols may be considered to have the following general formula in which R is the residue of the polyhydric alcohol which may contain unreacted hydroxyl groups, X indicates one or more of the epoxy ether groups attached to the alcohol residue, y may be one or may vary in difierent reaction products of the reaction mixture from zero to more than one, and Z is one or more, and X+Z, in the case of products derived from polyhydric alcohols containing three or more hydroxyl groups averages around two or more so that the reaction product contains on the average two or more than two terminal epoxide groups per molecule.

The internal epoxy group materials referred to above may be exemplified by the epoxidized esters of the polyethylenically unsaturated monocarboxylic acids, such as epoxidized linseed, soyabean, perilla, oiticica, tung, walnut and dehydrated castor oil, methyl linoleate, butyl linoleate, ethyl 9,12-octadecadienoate, butyl 9,12,l5octadecatrienoate, ethyl elaeostearate, octyl 9,12-octadecadienoate, methyl elaeostearate, monoglycerides of tung oil fatty acids, monoglycerides of soyabean oil, sunflower, rapeseed, hempseed, sardine, cottonseed oil, and the like.

Another group of the internal epoxy-containing ma-- 7 di(2,3-epoxyoctyl) tetrahydrophthalate, di(4,5-epoxydodecyl) maleate, di(2,3-epoxybutyl) terephthalate, di(2,3-

hexyl 4,5-epoxyoctanoate, and the like.

Still another group of the epoxy-containing materials include epoxidized derivatives of' polyethylenically unsaturated polycarboxylic acids, such as, for example, 7dimethyl 8,9,12,13-diepoxyeicosanedioate, dibutyl 7,8,11,12-

t 8 epoxide product was found to have an average molecular weight of 850. and an epoxy equivalent weight at 408; This polyepoxide is characterized in the following table as Polyether A.

A second batch of polyepoxide was prepared in the same manner but was washed only with water. This polyepoxide is labelled Polyether B in the table.

A series of mixtures of these poly-epoxides containing 100 parts of a polyether and parts of phthalic anhydride was prepared. With some of these mixtures were mixed various amounts of acetamide or urea.

Each mixture was heated to 120 C. and the viscosity of the mixture determined with a rotating-paddle electricically-driven torsion type direct-reading viscometer. The time required for each mixture to cure to a viscosity of 1500 centipoises was determined. The times (t) required for the anhydride-amide-cured polyepoxides to reach 1500 centipoises are compared in the table with talllose required by the polyepoxides cured with anhydride one.

diepoxyoctadecanedioate, dioctyl 10,11- diethyl-8,9,l2,

Polyether Time to 1,500 cp. Without Amide ti),

Minutes Reduction in t Tune Minutes 140 acetamide.--

. alcohol and/or unsaturated polycarboxylic acid or anhydride'groups, such as, for example, the polyester obtained' by reacting 8,9,12,13-eicosadienedioic acid with ethylene glycol, the polyester obtained by reacting diethylene glycol with 2-cyclohexene-1,4-dicarboxylic acid and the like, and mixtures thereof.

Another group comprises the epoxidized polymers andcopolymers of diolefins, such as butadiene. Examples of this include, 7 among others, -butadiene-acrylonitrile copolymers"(Hycar rubbers), butadiene-styrene copolymers and the like.

1 To illustrate the manner inwhich the invention may be carried out, the following example is given. his to be understood, however, that the example is for the purpose of illustration and the invention is not to be regarded as limited to any of the specific materials or conditions recited therein. The parts described in the example, are by weight" g s 7 Example I A polyepoxide :was'prepa-red by condensing 2,2 -bis- (4hydroxyphenyl) propane with epichlorohydrin in a ratio of 1:1.6; in the presence of an' aqueous medium kept just colorless to phenol phthaleinby the addition of 30% sodium-hydroxide; The reaction was stirred and maintained under nitrogen while being heated to 90-110' C. At the end of the reaction'the organic phase 'was recovered, cooled and treated with successive washes of water, dilute hydrochloric acidi'and water. The poly- We claim as our invention: 7

1. A process for producing a resinified product which consists of mixing and reacting a polyepoxide having vicinal epoxy groups with 10% to 80% by weight, based on the polyepoxide, of a polycarboxylic acid anhydride and 0.05% to 15% by weight, based on the polyepoxide, of an amide of the group consisting of urea, 'formamide, acetamide, propionamide, n-butyramide, phthalamide, salicylamide, naphthamides, adipamide, benzarnide, 'benzene sulfonamide and toluene sulfonarnide.

2. A process for producing a resinified product which consists of mixing and reacting a polyeopoxide having amide. Y 6. A process as in claim 2 where the amide is benzamide.

sulfonarnide. 7

References Cited in the file of this patent UNITED STATES PATENTS 2,324,483 Castan July 20, 1943 2,528,360 Greenlee Oct. 31, 1950 2,637,715 Ott May 5,1953 2,713,569 Greenlee V July 19, 1955 2,773,043. Zukas pe 1956 5. A process'as in claim 2 wherethe 'a 'de is acet- 7. A process as in claim 2 where the amide is benzene 

1. A PROCESS FOR PRODUCING A RESINIFIED PRODUCT WHICH CONSISTS OF MIXING AND REACTING A POLYEPOXIDE HAVING VICINAL EPOXY GROUPS WITH 10% TO 80% BY WEIGHT, BASED ON THE POLYEPOXIDE, OF A POLYCARBOXYLIC ACID ANHYDRIDE AND 0.05% TO 15% BY WEIGHT, BASED ON THE POLYEPOXIDE, OF AN AMIDE OF THE GROUP CONSISTING OF UREA, FORMAMIDE, ACETAMIDE, PROPIONAMIDE, N-BUTYRAMIDE, PHTHALAMIDE, SALICYLAMIDE, NAPHTHAMIDES, ADIPAMIDE, BENZAMIDE, BENZENE SULFONAMIDE AND TOLUENE SULFONAMIDE. 